IASF Bologna AGILE Observation of Terrestrial …...IASF Bologna III Fermi Symposium, Rome, 9/5/2011...
Transcript of IASF Bologna AGILE Observation of Terrestrial …...IASF Bologna III Fermi Symposium, Rome, 9/5/2011...
IASF Bologna
III Fermi Symposium, Rome, 9/5/20111
AGILE Observation ofTerrestrial gamma-Ray Flashes
Martino Marisaldi (INAF-IASF Bologna) on behalf of the AGILE Team
III Fermi Symposium
Rome, May 9-12 2011
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Outline AGILE TGF detection
capabilities in context Characteristics of the AGILE
TGF sample TGFs and global lightning
activity High energy results:
Localization of TGFs ingamma-rays from space
High energy spectrum
Credit: Alan Stonebraker
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Operating TGF detectors
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RHESSI
Fermi-GBM 12xNaI
Fermi-GBMNaI
GBM 2xBGO
GBM BGO
AGILE-MCAL AGILEGRID
Data from: Smith et al. (2002), Meegan et al. (2009), Labanti et al. (2009), Tavani et al. (2009)
Effective Area vs. Energy
LAT ?
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30 CsI(Tl) bars with Photodiode readout 1400 cm2 geometrical area ~300 cm2 effective area @ 1 MeV 330 keV – 100 MeV energy range 14% energy resolution FWHM @ 1.3 MeV 2 µs timing accuracy in photon-by-photon mode Clever, fully-programmable trigger logic on timescales from 8s to 16ms, 1ms and 300µs
The AGILE payload
40 cmLabanti et al., NIM A (2009): instrument paperFuschino et al., NIM A (2008): trigger logicMarisaldi et al., A&A (2008): GRB detectionsMarisaldi et al., JGR (2010): TGF detections
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MCAL TGF detection rate> 250 class A TGFs + ~130 class B TGFs since June2008
34 TGFs Published in M. Marisaldi et al.,J. Geoph. Res., 115, A00E13, 2010.
1ms triggeronset
After enteringSpinning mode
~10 TGF/monthsince Mar.'09~10 class A TGF/month~ 5 class B TGF/month
24 months 1st AGILE TGFcatalog in preparation
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The AGILE TGF sample
Average propertiesA AND B class:
Number of counts =14 +/- 9
Duration (=(0.8 +/- 0.4) ms
Energy =(4.0 +/- 1.7) MeV
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LIS/OTD global lightning distribution (10 Years of data)0.5 x 0.5 deg per bin
Flash rate [fl/km-2/year]
MCAL exposure [Seconds per bin] (Mar 2009-Feb 2010)Trigger logic really active2.5 x 1.0 deg [lon x lat]
Lightning distributionmultiplied by the MCAL exposure
to direct comparison with 12 Months of AGILE TGFs
LIS-OTD high resolution full climatology available athttp://thunder.msfc.nasa.gov/
For more information see the poster by F. Fuschino on May 11-12
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Imaging TGFs in gamma raysSearch for GRID events in temporal coincidence with 119MCAL TGFs detected between Jun. 2008 – Dec. 2009
12 σsignificance
13 GRID events within 2 ms from TGFs T0!
Albedo bkg
Forward Reverse
4 6
3
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Geographical distribution
AGILE footprintGRID g projection
GRIDpointing
Reverse eventdirection(TGF source)
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TGF 12809-19 in details(2010 Oct. 16 20:44:55 UT)
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γ-ray source
GOES IR image ~5 minutesbefore TGF
TRMM-LIS pass ~1 hourbefore TGF
Cre
dits
: B. C
arls
on, U
niv.
Ber
gen
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Geographical distribution
Event clustering at < 400 km from AGILE footprintConsistency with pervious detections based on RHESSI TGFs and sferics(Cummer et al., GRL 2005, Cohen et al., GRL 2010)Results published in Marisaldi et al., Phys. Rev. Letters 105, 128501 (2010)
Cohen et al., GRL 2010
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Cumulative spectrum110 TGFs 1806 photons 142 γ E> 10 MeV 26 γ E> 20 MeV
Results published in Tavani et al., Phys. Rev. Letters 106, 018501 (2011)
RREA cutoffpowerlaw model
significantdetection of γ >40 MeVuneplained bystandard RREAmodel: challengefor emissionmodels
Broken powerlawmodel β = -2.7
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High energy events
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Conclusions AGILE is an important instrument for TGF science:
− energy range extended up to 100 MeV− the only one with <1ms trigger logic− photon-by-photon with µs timing− ~equatorial orbit
AGILE detects ~10 TGFs / month with current selection criteria.Rate can be 50% increased with improved offline selections
7% TGFs can be localized in space by means of the AGILEgamma-ray imager.
Energy spectrum seems harder than previously expected,challenging current theoretical models.
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THANK YOU!
Credit: Alan Stonebraker
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Extra slides
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MCAL high energy calibration
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Giuliani et al., ApJL 708 (2010) L84
GRB 090510
prompt Extended emission
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Terrestrial Gamma-ray Flashes(TGF)
Gamma-ray flashes with incoming direction compatible with the Earthsurface.
Few millisecond typical duration; hard spectrum (up to tens MeV)
Discovered by BATSE (Fishman et al., Science, 1994) and observedby RHESSI up to 20 MeV (Smith et al., Science, 2005)
Clearly associated to lightning discharges during thunderstorms bymeans of correlation with VLF sferic waves detection on ground (Inanet al., GRL, 1996; Cummer et al., GRL, 2005)
>2008: Observed by AGILE and Fermi-GBM
2009: AGILE reports energy up to 40MeV (Marisaldi et al., JGR2010)
Geophysical phenomena observed from space by instrumentsdesigned for gamma-ray astrophysics
Challenging detection: timing and energy range are key issues
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~ 70 TGF detected on 9life-Yearstypically 100 counts/TGF
Main limitations:
- On-Board Trigger Logicperformances (shortertimescale 64ms)
- Large statistics BUTonly 4 energy bins fortime-tagged eventsFishman et al., Science, 1994
1994: BATSE discovery of TGF
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2005: RHESSI detectionup to 20 MeV
TGF Distributionwith lighting frequencyper km2 per Year
Smith et al., Science, 2005
Contiuous time-tagged event list NO ON-BOARD TRIGGER LOGIC 10– 20 TGF per month Typically 20-30 counts/TGF ~800 TGFs reported in the 1st RHESSI TGFcatalog (Grefenstette et al., JGR, 2009)
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RREA Production model
Dwyer and Smith, GRL (2005) Carlson, Lehtinen and Inan (2007)
Relativistic Runaway ElectronAvalanche (RREA) with relativisticfeedback (Dwyer 2008)
Bremsstrahlung + Compton scattering
RHESSI cumulative spectrum iscompatible with a production altitudeof 15-21 km (just above tropicalthunderstorms)
Still hint for individual spectralvariability: differences in productionaltitudes or viewing angle?
BATSE events seem produced athigher altitude (two differentpopulations?) but discrepancy isreduced if dead-time effects areproperly accounted for (Grefenstetteet al., 2008; Ostgaard et al., 2008)
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Why AGILE is goodfor TGF science?
MCAL energy range is extended up to 100 MeV: probingthe high energy tail of the TGF spectrum
Efficient trigger at ms and sub-ms time scale (the TGF timescale): not biased toward brightest events
segmented independent detectors: low dead time andpile-up
photon-by-photon data download for triggered events with2µs time resolution
<100µs absolute timing accuracy: mandatory for sfericscorrelation
AGILE orbit at 2.5° inclination is optimal for mapping theequatorial region, where most of the events take place, withunprecedented exposure
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Recent developments
Observations− space observations by Fermi and AGILE− airplane observations (the ADELE experiment)
Climatology− RHESSI TGFs vs. lightning occurrence and
tropopause height (Smith et al., JGR, 2010) Modeling
− relativistic feedback, flux and dose estimates(Dwyer 2008, 2010)
− VLF signature of relativistic runaway electrons(Fullekrug et al., 2010)
New missions− ASIM, Taranis, Firefly
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MCAL Burst Trigger Logic Long (SW evaluated) time windows: 64ms, 256ms, 1.024s, 8.192s 4 spatial zones and 3 energy ranges
Short (HW evaluated) time windows: sub-millisecond, 1ms, 16ms First trigger logic at ~1ms time scale
Very flexible: more than 2000 parametersfor full configuration; dedicated look-uptables to accept/reject triggers Current threshold settings:
16ms: >22 counts 1ms: >10 counts 293ms: > 8 counts
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Trigger selectionKey parameter: Hardness Ratio
HR = (n. evt E>1.4 MeV) / (n. evt. E<1.4 MeV)
Selection criteria to reject known instrumental triggers: HR > 0.5
Knowninstrumentaltriggers
Knowninstrumentaltriggers
All othertriggers
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AGILE vs RHESSI:longitude and local time
AGILERHESSI
1st RHESSI TGF catalogGrefenstette et al., JGR,(2009)
selected RHESSI TGFs ina +/- 2.5° latitude belt(like AGILE orbit) T0 < 1st
Jan. 2006: 84 TGFs
Longitude and local timedistributions arecompatible
sharp cut on western Africa
double peaked featureon South East Asia
late afternoonoccurrence peak
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Trigger 11026-1 in details
<0.7 MeV
0.7-1.4 MeV
1.4-2.8 MeV
>2.8 MeV
All range
Light curve Position distribution Energy vs time
Bar address vs time
40 MeV
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Single TGF energy spectrum
011026-1
cutoff powerlawfit the 0.5-30 MeV rangeα = -0.6 +/- 1.0E0 = (5.4 +/- 3.0) MeVred. χ2 = 1.1 (5 d.o.f.)
Spectral parameters are poorly constrained due to limitedstatistics
011026-1 spectrum is compatible with cumulativespectrum
Need more bright events
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AGILE-MCAL vs RHESSI
Aeff,R =~50 cm2 @1MeV
Smith et al., (2002)
Labanti et al., (2009)
Total Aeff,M ~300 cm2 @1MeV
Photopeak Aeff,M ~110 cm2 @1MeV
MCAL RHESSI
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AGILE vs RHESSI:cumulative spectrum
Spectral shapes are compatibleAGILE model fits well RHESSI data tooBUT AGILE seems to select a harder population
cutoff powerlawfit the 0.5-30 MeV rangeα = 0.4 +/- 0.2E0 = 6.6 +/- 1.2 MeVred. χ2 = 1.5 (34 d.o.f.)
cutoff powerlawfit the 0.5-20 MeV rangeα = -0.1 +/- 0.3E0 = 4.4 +/- 1.2 MeVred. χ2 = 0.8 (18 d.o.f.)
AGILE RHESSI
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AGILE vs RHESSI:cumulative spectrum
Spectral shapes are compatibleBUT AGILE seems to select a harder population
E cutoff vs. alpha confidence intervals
AGILE RHESSI
3σ
2σ
1σ
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AGILE vs Fermi-GBM
12 × NaI + 2 × BGO
Fermi TGF #7 AGILE TGF 11026-1
Fermi:+ larger effective area and lower threshold: morestatistics on single events- trigger on time >=16ms: less events, brightness bias(AGILE triggers on >=290µs)
from A. Von Kienlin, presentation at the 7th AGILE WS
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Imaging TGFs from space?
MCAL detected TGFphotons up to 40 MeVand possibly above
So, why not looking fordetections in the AGILEgamma-ray imager(GRID) sensitive above20 MeV?
It would be the firstdirect localization ofTGFs in gamma-rays
GRIDpointing
FOV 120°
MCAL non-imagingFOV 4π
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TGF
g
ON
-BO
AR
D A
LBED
O F
ILTE
RIN
G
Imaging TGFs from spacewith AGILE GRID
GRID
pointing
FOV 120°
MCAL non-imaging
FOV 4π
EA
RTH
Two ways to bypass it...
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TGF
γ
Imaging TGFs from spacewith AGILE GRID
GRID
pointing
FOV 120°
MCAL non-imaging
FOV 4π
EA
RTH
1. Albedo filtering disabled~ 100 days between 2008 – 2009for test purposes
Forward events.Cannot be default because of telemetry limitations
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2. Sometimes the albedo filtercan “mistake” a track with thecomplementary one
ON
-BO
AR
D A
LBED
O F
ILTE
RIN
G
Imaging TGFs from spacewith AGILE GRID
EA
RTHGRI
Dpo
intin
g
FOV
120°
MCA
L no
n-im
agin
gFO
V 4π
TGF
γ
So, events coming from the Earth canbe accepted by the on-board filter andsent to telemetry: Reverse events
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Do GRID photons come directlyfrom the production region?
TGF production
region
AGILE
good
AGILE
bad
TGF production
region
Comptoninteraction
the incoming photon direction tracks theproduction region.
the incoming photon direction DOES NOTtracks the production region. No way to beaware of it. Is it probable???
15-20 km
540 km
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Do GRID photons come directlyfrom the production region?
Compton and pair production cross section inair become equivalent at ~25MeV:Compton interaction for low-energy GRIDevents cannot be ignored <3% probability to scatter above 40 km: the
GRID photon tracks the source within theangular resolution
15-20 km
540 km
1.00E+000 1.00E+001 1.00E+002 1.00E+003
1.00E-003
1.00E-002
1.00E-001
gamma cross section in air
Compton Scatter.Nuclear Pair Prod.Total
Energy (MeV)
cm2/
g
AGILE
good
TGF production
region
Comptoninteraction
40 km
AGILE
bad
TGF production
region
Comptoninteraction
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Implications forproduction models
50 MeV
High energy photons track well the electric field orientation at the sourceA new tool to probe remotely the production site electric field
Roussel-Doupre et al.Sp. Sci. Rev. 2009